1. Field of the Invention
The present invention relates to an emitting direction control apparatus that changes the emitting direction of lamps like the headlamps of a vehicle, such as an automobile. Particularly, the present invention relates to an emitting direction control apparatus wherein a stepping motor is employed as a drive source of a drive mechanism that changes emitting directions.
2. Related Art
In order to ensure safe driving for automobiles, emitting direction control apparatuses have been provided that adjust the emitting directions of lamps, particularly headlamps, respectively in the vertical direction, and in the horizontal direction. The control apparatus for the vertical direction changes lighting axes of the headlamps vertically, so that these axes are in a predetermined direction, regardless of whether the inclination of the automobile is changed in accordance with the condition of loads or the condition of occupants in the automobile. The control apparatus for the horizontal direction changes the lighting axes of the headlamps in the traveling direction in accordance with a steering angle when an automobile is being driven along a curved road or around a corner in a road. Both control apparatuses include: a drive mechanism for changing the lighting axes of headlamps and a controller for controlling the drive mechanism; and based on the output of a sensor that detects the inclination of an automobile, or a steering angle, the controller permits the drive mechanism to appropriately change the lighting axes.
In these emitting direction control apparatuses, a stepping motor is employed as the driving source for the drive mechanism in order to control the lighting axes at each predetermined angle. The stepping motor is a motor that is rotated, step by step, at an angle that corresponds to the number of pulses of an input pulse signal, and to control the lighting axes at predetermined angle positions, the controller need only transmit, to the stepping motor, a number of pulse signals that correspond to the lighting axis angle of the adjustment. Further, the drive mechanism rotates a mechanism that reduces the speed of rotation of the stepping motor to change the lighting axis angles of the reflector of a lamp and a lamp body.
For an emitting direction control apparatus of this type, a so-called initialization is performed, wherein the stepping motor is set at a predesignated initial angular position (hereinafter referred to as an initial position) in order to very accurately control the lighting axis of the lamp. After the initialization has been performed, the stepping motor is rotated from the initial position, at an angle based on the number of steps, and the angle of the lighting axis is deflected. According to one method for performing the initialization, an angular sensor for detecting the lighting axis angle of a lamp is provided for the drive mechanism, the rotation position of the stepping motor is identified based on the output of the angular sensor, and the stepping motor is set at the initial position based on the rotation position. However, the angular position of the lighting axis detected by the angular sensor is a position obtained by reducing the rotational, angular velocity of the stepping motor. Further, while taking a detection error of the angular sensor, i.e., the resolution, into account, since the resolution is equivalent to about 100 steps, through the conversion of an angle into a single step of the stepping motor, it is extremely difficult for the stepping motor to be accurately set in the initial position when the angle of the angular axis is detected by the angular sensor.
According to another method used for initialization, the stepping motor is rotated in one direction, and is bumped to a maximum angular position (hereinafter this position is called a bumped position), which is a limiting position for the drive mechanism, whereat the lighting axis can be deflected in one direction. And the position whereto the stepping motor is rotated a predetermined number of steps from the bumped position is regarded as the initial position. According to this method, since the limiting position for the drive mechanism is uniquely defined, the initial position of the stepping motor can be precisely designated. This method is proposed in JP-A-2004-343987. Further, in JP-A-10-326505, a technique is proposed whereby initialization is performed by moving the stepping motor to the bumped position.
According to these initialization methods, when the stepping motor has been rotated to the bumped position in one direction, the stepping motor is reversely rotated a small angle by a repulsive force, the result of the bumping, and a rebound vibration occurs by repeating this phenomenon. This rebound vibration is gradually reduced as time elapses; however, a little time is required for the vibration to settle completely at “0”, and because of this time (hereinafter called a rebound time), the initialization period for setting the initial position is required. Especially since the stepping motor is rotated rapidly in order to deflect the lighting axis at a high speed, the rebound vibration is remarkable, and the rebound time is extended and can not be ignored. According to the technique in JP-A-2004-343987, the stepping motor must be rotated in the reverse direction when the rebound is removed, and accordingly, the initialization period is extended. According to the technique in JP-A-10-326505, in order to resolve the rebound problem, in a state wherein rebound occurs, i.e., in a state wherein the stepping motor is rotated beyond the bumped position, the rotational speed of the motor is reduced and rebounding at the bumped position is suppressed, so that the rebounding period is shortened and the initialization period is reduced.
However, since the technique in JP-A-10-326505 is not one for removing rebound vibration, the rebounding period can not be “0”, and the reduction during the initialization period is limited. Further, since the stepping motor is rotated at a high speed, the repulsive force produced by the rebounding is added as an impact force to the stepping motor. Thus, the stepping motor tends to be damaged and to be deteriorated, and its service life is shortened.